JPH0912785A - Polyolefin pipe - Google Patents

Abstract

PURPOSE: To produce a polyolefin pipe, having a gradual reduction in concentration of an antioxidant in the pipe, capable of suppressing the oxidation of the resin for a long period, having a high mechanical strength of a pipe outer shell and useful as a piping material for hot water supply, etc., by forming an inner layer of a specific polyolefin-based resin composition. CONSTITUTION: This polyolefin pipe is obtained by forming an inner layer having 1-2mm thickness of a polyolefin-based resin composition containing 0.3-3 pts.wt. antioxidant having 2000-5000 molecular weight [e.g. dimethyl succinate-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate] added to 100 pts.wt. polyolefin-based resin such as a (cross- linked)polyethylene, polypropylene or poly(1-butene).

Description

Detailed Description of the Invention

[0001]

This invention relates to polyolefin pipes.

[0002]

2. Description of the Related Art Pipes made of polyolefin resins such as polyethylene, polypropylene, and polybutene are used as hot water supply pipes. No change is observed, but the mechanical strength is lowered due to thermal oxidation from the inner surface, which causes the breakage of the pipe. Therefore, various heat stabilizers and antioxidants are added to polyolefin resins to manufacture pipes.

Examples of pipes such as hot water supply pipes in which the above-mentioned antioxidant is added to a polyolefin resin are, for example, Japanese Patent Publication No.
As described in Japanese Patent Publication No. 3-42932, poly-
With respect to 100 parts by weight of 1-butene, (A) general formula,

[0004]

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0.05 to 1.0 part by weight of at least one compound represented by the formula (wherein R is an alkyl group having 1 to 18 carbon atoms or an arylalkyl group),
And (B) 0.1 to 1.0 part by weight of at least one compound selected from the following hindered phenol group, (a) 1,3,5-trimethyl-2,4,6-tris ( 3,5-di-tert-butyl-4-hydroxybenzyl)
Benzene (b) 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylphenyl) isocyanurate (c) Tris (3,5-di-tert-butyl-4-hydroxyphenyl) ) Isocyanurate (d) n-octadecyl-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate (e) Bis (3,5-di-tert-butyl-4-hydroxybenzoylphosphonic acid) Nickel salt of monoethyl ester (f) 2,2-dihydroxy-3,3′-di (α-methylcyclohexyl) -5,5′-dimethyl-dimethylmethane (g) 4,4-thio-bis (3-) Methyl-6-tert-butyl-phenol) (h) 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butyl-phenyl) butane (i) Tetrakis [methylene-3 3,5-di - tert-butyl-4-hydroxyphenyl) propionate) for methane by blending water supply and hot water supply pipe poly-1-butene resin composition is disclosed.

However, in any of the formulations disclosed in JP-B-63-42932, the compounds (A) and (B) migrate mainly to the inner surface of a polyolefin resin tube such as poly-1-butene resin. However, it elutes out of the system in a relatively short time together with the fluid flowing therein, and it is difficult to use it for a long time in a piping system that requires heat resistance.

[0007] These antioxidants generally depend on the kind and combination thereof, but in the hot water supply pipe, when the concentration in the blended resin becomes 0.001% by weight or less, the oxidation of the resin starts and the mechanical strength decreases. It was clarified by the investigation of the present inventors. Oxidative deterioration of the polyolefin pipe inner layer, when the dissolved oxygen in hot water diffuses into the polyolefin layer to compete with the antioxidant, and the concentration of the antioxidant decreases below the above-mentioned certain concentration due to consumption or elution of the antioxidant. Oxidation occurs. In the water supply / hot water supply pipe, it is the inner surface of the pipe that has the lowest concentration of antioxidant.
The carbonyl group is first discovered in that part.

Further, the diffusion rate of the antioxidant in the polyolefin layer depends on its molecular weight, and the diffusion coefficient corresponding to the molecular weight 500 of an ordinary average antioxidant has a molecular weight of 200.
It is more than 6 times the diffusion coefficient corresponding to 0. On the other hand, the migration rate of the antioxidant from the polyolefin layer also depends on the molecular weight between the antioxidants of the same system, and the migration rate is higher as the molecular weight is smaller. Further, the compatibility of the antioxidant with the polyolefin also depends on the molecular weight between the antioxidants of the same series, and the compatibility decreases with an increase in the molecular weight.

As described above, the present technology for imparting antioxidant properties to polyolefin pipes is still insufficient, and there is no pipe of polyolefin resin alone that can withstand long-term use in the fields of hot water supply, air conditioning, and chemical plants. There is a strong demand for improvement in heat resistance.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and an object of the present invention is to provide a polyolefin pipe capable of withstanding long-term use in the fields of hot water supply, air conditioning, and chemical plants.

[0011]

The present invention according to claim 1 has a thickness of 1 to 3 in which 0.3 to 3 parts by weight of an antioxidant having a molecular weight of 2000 to 5000 is added to 100 parts by weight of a polyolefin resin. A gist of a polyolefin pipe is that an inner layer made of a polyolefin resin composition having a thickness of 2 mm is formed.

In the present invention, the molecular weight is 2000 to 5000.
When the molecular weight of the antioxidant is less than 2000, the migration from the polyolefin resin layer is large, and when the molecular weight exceeds 5000, the compatibility with the polyolefin resin decreases. In either case, it is difficult to impart long-term heat resistance to the polyolefin pipe.

The antioxidant has a molecular weight of 2000.
It is not particularly limited as long as it is an antioxidant of up to 5000, but for example, dimethyl succinate 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-
Tetramethylpiperidine polycondensate, poly [{6- (1,
1,3,3-tetramethylbutyl) amino-1,3,5
-Triazine-2,4-diyl} (2,2,6,6-
Tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino}], N, N'-bis (3-aminopropyl) ethylenediamine-2,4- Bis [N-butyl-N
A hindered amine high molecular weight type antioxidant such as-(1,2,2,6,6-pentamethyl-4piperidyl) amino] -6-chloro-1,3,5-triazine condensate is preferably used. .

The polyolefin resin is not particularly limited, but examples thereof include polyethylene (crosslinked polyethylene), polypropylene, poly (1-butene) and the like.

The antioxidant is added in an amount of 0.3 to 3 parts by weight with respect to 100 parts by weight of the polyolefin resin. If the amount is less than 0.3 parts by weight, the polyolefin resin is oxidized. If the addition amount exceeds 3 parts by weight, the effect of suppressing the oxidation of the polyolefin-based resin is saturated, and even if it is added more than that, no new effect is obtained, and it is obtained. Reduces the mechanical strength of polyolefin pipes.

The polyolefin pipe of the present invention is formed with an inner layer having a thickness of 1 to 2 mm, which is made of the polyolefin resin to which the above-mentioned antioxidant is added. If the concentration of the antioxidant that can withstand use cannot be maintained and the thickness of the inner layer exceeds 2 mm, the effect of suppressing the oxidation of the polyolefin-based resin for a long period of time will be saturated, and even if the thickness exceeds this value, Not only cannot obtain such effects, but also lowers the mechanical strength of the obtained polyolefin pipe.

The polyolefin pipe of the present invention includes a pipe main body made of a cylindrical long body and various cheeses, elbows, sockets, bends, curved pipes, flanges, valves and the like used for piping the pipe main body for various purposes. It also includes piping members.

The means for forming an inner layer having a thickness of 1 to 2 mm, which is made of the polyolefin resin to which the above-mentioned antioxidant is added, on the polyolefin pipe is not particularly limited, but, for example, the commonly used two-layer extrusion is used. A polyolefin-based resin prepared by compounding a normal polyolefin pipe on the outside so that the thickness of the polyolefin-based resin added with the above-mentioned antioxidant on the inside becomes a thickness determined within the range of 1 to 2 mm by the machine. A two-layer extrusion molding method of a pipe in which the thickness of the pipe is adjusted to a standard value determined for each diameter by adding the inner layer is preferably used. For the pipe member, the two-layer injection molding method is preferably used as in the above. Further, the above-mentioned antioxidant-added polyolefin resin layer may be provided with a concentration gradient, if necessary, to form a multilayer of two or more layers, and the antioxidant concentration on the inner surface of the polyolefin pipe may be averaged over time. .

[0019]

The polyolefin pipe of the present invention has a molecular weight of 2000 to 50 per 100 parts by weight of the polyolefin resin.
Thickness of 0.003 added with 0.3 to 3 parts by weight of antioxidant
Since the inner layer made of a polyolefin resin composition having a thickness of up to 2 mm is formed, the concentration of the antioxidant on the inner surface of the polyolefin pipe is gradually lowered, and the concentration of the antioxidant of the polyolefin resin is maintained for a long time. In addition, since most of the thickness of the polyolefin pipe forms an outer shell made of a mixture of ordinary polyolefin pipes with high mechanical strength, it can be used as a hot fluid in the fields of hot water supply, air conditioning, chemical plants, etc. It can be used as a piping material that will be in contact for a long time.

[0020]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Linear low density polyethylene (manufactured by Mitsubishi Chemical Co., density 0.936 g / cm ³ , MFR5.
0) silane-crosslinked polyethylene resin (MFR0.
8) 100 parts by weight, for the inner layer, a hindered amine high molecular weight type antioxidant (manufactured by Ciba Geigy, trade name: CHIMASSORB 944, molecular weight 2500)
0.5 part by weight and 0.1 part by weight of phosphorus-based antioxidant are added, and 0.1 part by weight of the above-mentioned hindered amine-based high molecular weight type antioxidant and phosphorus-based antioxidant (commercially available from Ciba Geigy Co., Ltd., product Name: IRGAFOS 168) 0.1 parts by weight of polyethylene was added to a polyethylene having a thickness of 4.5 mm and an inner diameter of 50 mm at a molding temperature of 200 ° C. using a two-layer extruder having a diameter of 75 mm. A pipe was made.

Example 2 Polyethylene was prepared in the same manner as in Example 1 except that the amount of the hindered amine type high molecular weight type antioxidant added in Example 1 was changed from 0.5 parts by weight to 2.0 parts by weight. A pipe was made.

Comparative Example 1 A phenolic antioxidant (manufactured by Ciba-Geigy, trade name: IRGANOX1076, molecular weight 531) was added to 100 parts by weight of the polyethylene resin obtained by silane-crosslinking the linear low-density polyethylene of Example 1.
0.35 parts by weight and 0.2 parts by weight of a sulfur-based antioxidant (manufactured by Ouchi Shinko Chemical Co., Ltd., trade name: Nocrac400) were added, and a molding temperature of 200 ° C. was used using an extruder having a diameter of 75 mm.
Then, a polyethylene pipe having a thickness of 4.5 mm and an inner diameter of 50 mm was produced.

Comparative Example 2 In place of the antioxidant of Comparative Example 1, 0.2 parts by weight of the hindered amine high molecular weight type antioxidant used in Example 1 and the phosphorus-based antioxidant 0.
A polyethylene pipe was produced in the same manner as in Comparative Example 1 except that 1 part by weight was added.

Comparative Example 3 In place of the antioxidant of Comparative Example 1, 5.0 parts by weight of the hindered amine type high molecular weight type antioxidant used in Example 1 and the phosphorus type antioxidant 0.1.
A polyethylene pipe was produced in the same manner as in Comparative Example 1 except that 1 part by weight was added.

Example 3 100 parts by weight of polypropylene (manufactured by Tokuyama Corporation, MFR1.5) was used as an inner layer for a hindered amine high molecular weight type antioxidant (manufactured by Ciba Geigy, trade name: TINUVIN 622, molecular weight 3).
000) 0.5 parts by weight and sulfur-based antioxidant (supra)
0.2 part by weight is added, 0.1 part by weight of the hindered amine high molecular weight type antioxidant and 0.1 part by weight of the sulfur type antioxidant (described above) are added for the outer layer, and the caliber is 75
mm 2-layer extruder, molding temperature 230 ° C., inner layer thickness 1.0 mm, thickness 4.5 mm, inner diameter 50 mm
The polypropylene pipe of was produced.

Example 4 Polypropylene was prepared in the same manner as in Example 3 except that the amount of the hindered amine high molecular weight type antioxidant added in Example 1 was changed from 0.5 parts by weight to 2.0 parts by weight. A pipe was made.

Comparative Example 4 100 parts by weight of the polypropylene resin of Example 3 was added to a hindered phenolic antioxidant (manufactured by Ciba-Geigy, trade name: IRGANOX1).
010, molecular weight 1178) 0.35 parts by weight and a sulfur-based antioxidant 0.2 parts by weight were added, and an extruder having a caliber of 75 mm was used at a molding temperature of 230 ° C., a thickness of 4.5 mm, and an inner diameter of 5
A 0 mm polypropylene pipe was made.

Comparative Example 5 In place of the antioxidant of Comparative Example 4, 0.2 parts by weight of the hindered amine high molecular weight type antioxidant used in Example 3 and 0.2 part by weight of the sulfur type antioxidant were used. A polypropylene pipe was produced in the same manner as in Comparative Example 4 except that the polypropylene pipe was added.

Comparative Example 6 In place of the antioxidant of Comparative Example 4, 5.0 parts by weight of the hindered amine type high molecular weight type antioxidant used in Example 3 and 0.2 part by weight of a sulfur type antioxidant were used. A polypropylene pipe was produced in the same manner as in Comparative Example 4 except that the polypropylene pipe was added.

A hot water aging test was conducted by passing hot water of 95 ° C. at a hot water pressure of 2 kg / cm ² through the polyethylene pipe and polypropylene pipe obtained in the above Examples and Comparative Examples. The sample was sampled at regular intervals, the test sample was cut open, and the state of embrittlement on the inner surface was observed. The results are shown in Table 1.

[0032]

[Table 1]

In the table, the arrow means the same as in the left column, and the crosslinked polyethylene pipe of the example is 33000 hours (about 4 years).
Although no change was found after the lapse of time, in the polypropylene pipes of the examples, the samples after 33,000 hours (about 4 years) had a whitish surface with diffuse reflection of light, and were in an oxidation state to the extent that surface pulverization occurred. there were. On the other hand, the cross-linked polyethylene pipe of the comparative example has 8760 in spite of the fact that the absolute amount of the compounding amount per unit weight is much larger than that of the example.
During the time (1 year) to 25,000 hours (about 3 years), cracks that could be visually confirmed appeared from the above-mentioned surface pulverization state, and the oxidation state was represented by the microcracks in the table. The polypropylene pipe of the comparative example is 8760 hours (one year) shorter than the cross-linked polyethylene pipe of the comparative example.
After about 17500 hours (about 2 years), the surface was powdered and was in the state of fine cracks and oxidation.

[0034]

EFFECT OF THE INVENTION Since the polyolefin pipe of the present invention is constructed as described above, the concentration of the antioxidant on the inner surface of the polyolefin pipe is gradually lowered, and the concentration of the antioxidant of the polyolefin resin is suppressed for a long time. It can be maintained and most of the thickness of the polyolefin pipe forms an outer shell consisting of a mixture of normal polyolefin pipe with high mechanical strength, so it can be used in hot water supply, air conditioning, chemical plant fields, etc. It can be used as a piping material that will be in contact with

Claims (1)

[Claims] 1. An antioxidant 0.3 to 3 having a molecular weight of 2000 to 5000 per 100 parts by weight of a polyolefin resin.
A polyolefin pipe, wherein an inner layer made of a polyolefin resin composition having a thickness of 1 to 2 mm, to which parts by weight are added, is formed.